Nucleic acid encoding the ba chain prodomains of inhibin and method for synthesizing polypeptides using such nucleic acid

ABSTRACT

DNA encoding the prepro inhibin α and β chains has been isolated. This DNA is ligated into expression vectors and used to transform host cells for the preparation of inhibin or activin. Also provided are prohormone domains and other inhibin α and β chain derivatives having therapeutic or diagnostic interest. The compositions provided herein are useful in the manipulation of fertility in animals.

This is a divisional application of copending U.S. Ser. No. 07/215,466,filed Jul. 5, 1988, U.S. Pat. No. 5,089,396, which is a divisionalapplication of U.S. Ser. No. 906,729, filed Dec. 31, 1986, U.S. Pat. No.4,798,885 which is a continuation-in-part application of U.S. Ser. No.827,710, filed Feb. 7, 1986, now abandoned, which is in turn acontinuation-in-part application of U.S. Ser. No. 783,910, filed Oct. 3,1985, now abandoned.

BACKGROUND

This invention relates to methods for making proteins in recombinantcell culture which contain the α or β chains of inhibin. In particular,it relates to methods for obtaining and using DNA which encodes inhibin,and for making inhibin variants that depart from the amino acid sequenceof natural animal or human inhibins and the naturally-occurring allelesthereof.

Inhibin is a protein produced in the gonad which acts specifically atthe pituitary level to inhibit the secretion of follicle-stimulatinghormone (FSH). The existence of inhibin was first postulated byMcCullagh in 1932 ("Science" 76: 19-20). Such preferential regulation ofthe gonadotropin secretion has generated a great deal of interest andhas prompted many laboratories in the past fifty years to attempt toisolate and characterize this substance from extracts of testis,spermatozoa, rete testis fluid, seminal plasma and ovarian follicularfluid, using various bioassays. Although many reports have appeared inthe literature claiming the purification of inhibin-like material withmolecular weights ranging from 5,000 to 100,000 daltons, subsequentstudies have shown that these substances were not homogeneous, did nothave the high specific activity expected of true inhibin and/or failedto exhibit the molecular characteristics of inhibin as described herein(de Jong, InhibinFactor Artifact, "Molecular & Cellular Endocrin." 13:1-10 (1979); Sheth et al., 1984, "F.E.B.S." 165(1) 11-15; Seidah et al.,1984, "F.E.B.S." 175(2):349-355; Lilja et al., March 1985, "F.E.B.S."182(1):181-184; Li et al., June 1985, "Proc. Nat. Acad. Sci. USA"82:4041-4044; Seidah et al., "F.E.B.S." 167(1):98-102; and Beksac etal., 1984, "Intern. J. Andrology" 7:389-397).

A polypeptide having inhibin activity was purified from bovine and ovinefollicular fluid (PCT 86/00078, published Jan. 3, 1986). This proteinwas reported to have a molecular weight of 56,000±1,000 on SDS-PAGE andwas dissociable into two subunits having apparent molecular weights of44,000±3,000 and 14,000±2,000. Amino terminal sequences for each subunitwere described.

Two proteins both having a molecular weight of about 32,000 daltons andhaving inhibin activity have been successfully isolated from porcinefollicular fluid. Purification of porcine inhibin to substantialhomogeneity, i.e., about 90% by weight of total protein in the fraction,was achieved through a combination of protein separation proceduresincluding heparin-Sepharose affinity chromatography, gel filtration andreverse-phase, high-performance liquid chromatography (RP-HPLC).

These proteins were isolated to substantial homogeneity from materialobtained from swine and are referred to as Protein A and Protein B. Eachprotein has a molecular weight of about 32,000 daltons (32K) and iscomposed of two polypeptide chains having molecular weights of 18,000and 14,000 daltons, respectively, the chains being linked together inthe hormonally-active protein by disulfide bonding. The amino-terminalamino acid residue sequence of the 18,000 dalton (18K) or alpha chain ofboth proteins was determined to beSer-Thr-Ala-Pro-Leu-Pro-Trp-Pro-Trp-Ser-Pro-Ala-Ala-Leu-Arg-Leu-Leu-Gln-Arg-Pro-Pro-Glu-Glu-Pro-Ala-Val.The amino-terminal amino acid residue sequence of the 14,000 dalton(14K) or beta chain of Protein A was determined to beGly-Leu-Glu-X-Asp-Gly-Lys-Val-Asn-Ile-X-X-Lys-Lys-Gln-Phe-Phe-Val-Ser-Phe-Lys-Asp-Ile-Gly-Trp-Asn-Asp-Trp-Ile-Ile-Alaand of Protein B was determined to beGly-Leu-Glu-X-Asp-Gly-Arg-Thr-Asn-Leu-X-X-Arg-Gln-Gln-Phe-Phe-Ile-Asp-Phe-Arg-Leu.Proteins A and B have been completely characterized. Each 32K proteinexhibits inhibin activity in that is specifically inhibits the basalsecretion of FSH but does not inhibit secretion of luteinizing hormone(LH). The individual chains were not hormonally active.

After the filing of the parent application hereto, inhibin B-chaindimers were shown to exist in follicular fluid as naturally-occurringsubstances, termed activin, which are capable of stimulating FSH releaseby rat anterior pituitary cells (Vale et al., 1986, "Nature" 321:776-779and Ling et al., 1986, "Nature" 321:779-782).

The amino acid sequence of the α and β chains of inhibin from humansremained unknown until the invention herein. The large quantities ofhuman follicular fluid required to parallel the studies conducted withanimal inhibins are not readily available, nor is there any assurancethat human and animal inhibins would be sufficiently similar thatpurification using a parallel procedure would be effective. Accordingly,methods are needed for determining the characteristics and amino acidsequence for human inhibin.

Also needed are economical methods for making the α and β chains ofinhibin in large quantities, preferably entirely and completely free ofproteins from the species homologous to the inhibin in question, whichinhibin preferably also is biologically active.

These and other objects will be apparent from consideration of theinvention as a whole.

SUMMARY

Nucleic acid now has been isolated and cloned in replicable vectorswhich encodes the mature porcine and human α and β chains of inhibin andtheir precursor prepro and pro forms. Sequencing of inhibin-encodingcDNA has led to the identification of prodomain regions locatedN-terminal to the mature inhibin chains that represent coordinatelyexpressed biologically active polypeptides. The prodomain regions orprodomain immunogens are useful in monitoring preproinhibin processingin transformant cell culture or in experiments directed at modulatingthe clinical condition or reproductive physiology of animals. Thus α orβ chain nucleic acid is used to prepare prodomain sequences from theprecursor forms of the inhibin chains, to transform host cells for therecombinant expression of mature inhibin α and/or β chains, and indiagnostic assays. In particular, regions from inhibin α and/or β chainsare expressed in recombinant cell culture by a method comprisingligating the nucleic acid encoding the region into a replicable vectorunder the control of a promoter, transforming a host cell with thevector, culturing the host cell and recovering the prodomain, activin orinhibin from the cultured cell. Inhibin, activin and prodomains producedby the method of this invention are entirely free of homologous sourceproteins and can be produced in biologically active form.

The nucleic acids identified herein encode the α, β_(A) and β_(B) chainsof porcine or human inhibin. Recombinant cells are transformed toexpress αβ_(A) or αβ_(B) inhibins, or to express β-chain heterodimers orhomodimers (which are collectively referred to in the literature asactivin). β-chain dimers as products of recombinant cell expression arefree of homologous proteins with which they ordinarily are associated innature.

Inhibin or activin and their nontoxic salts, combined with apharmaceutically acceptable carrier to form a pharmaceuticalcomposition, are administered to mammals, including humans, for controlof fertility. Administration of inhibin decreases fertility in femalemammals and decreases spermatogenesis in male mammals, andadministration of a sufficient amount induces infertility. Inhibin isalso useful in tests to diagnose infertility. Activin has been shown inthe literature to be capable of stimulating FSH release from pituitarycells and accordingly is useful as a fertility inducing therapeutic.

The method of this invention also facilitates the convenient preparationof inhibin, activin and prodomain variants having primary amino acidsequences and/or glycosylation differing from the native analogues, inparticular fusions of immunogenic peptides with inhibin, activin orprodomain sequences.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic representation of the porcine α-chain mRNA.Overlapping cDNA clones used in the sequence determination are shownabove the diagram of the mRNA structure. Black boxes on the 3' ends of λclones indicate that these clones were obtained by specific priming.Untranslated sequences are represented by a line, coding sequences areboxed. The unfilled portion represents the coding region for the signalpeptide and pro-sequences, and the cross-hatched area indicates the 134amino acid α-chain. The scale is in nucleotides from the 5' end of thelongest cDNA clone.

FIG. 1B shows the nucleotide and predicted amino acid sequence of theporcine inhibin α-chain precursor. Nucleotides are numbered at the leftand amino acids are numbered throughout. The amino acid sequenceunderlined was used to design a long synthetic DNA probe. The 364 aminoacid precursor includes a hydrophobic signal sequence, a pro-region, andthe mature α-chain (amino acids 231-364). The proteolytic processingsite Arg-Arg (black bar) immediately precedes the NH2-terminus of themature alpha chain. Several other putative dibasic processing sitespresent in the pro-region are indicated by open bars. The singlepotential N-linked glycosylation site is shown by the cross-hatched bar.The AATAAA box close to the 3' end of the mRNA is underlined.

FIG. 2A is a schematic representation of the porcine β_(A) and β_(B)subunit mRNAs with coding sequences boxed. The β_(A) and β_(B) subunits(dashed) are encoded towards the 3' end of the coding sequences. The 3'and 5' untranslated regions are shown as a line. The length of the 5'and 3' untranslated region of the βB subunit mRNA is inferred from thesize of the mRNA (FIG. 3) and its obvious similarity to the β_(A) mRNA.Tentative regions of the cDNAs are shown as dashes in the diagram. Therelative positions of the overlapping oligo-dT primed cDNA clones andthe randomly primed clones (λPINβ_(A) 5s, λPINβ_(B) 1s, and λPINβ_(B)2s) are indicated. The scale is in nucleotides from the 5' end of the4.5 kb mRNA.

FIG. 2B is the nucleotide sequence and deduced amino acid sequence ofthe porcine inhibin β-subunit precursors. The β_(B) sequence is alignedwith the β_(A) sequence for maximum homology. The NH₂ -termini of theβ-subunit precursors are indicated by bracket and arrows. Cysteineresidues are shaded, possible processing sites are indicated by openbars, and a potential glycosylation site is shown by the cross-hatchedbox. A very GC-rich region present 3' to the termination codon intronsequences is underlined and overlined in both sequences. Amino acidsequences used to design oligonucleotide probes are underlined, as isthe AATAAA polyadenylation signal. There was one nucleotide differencebetween λPIN-β_(A) 8 and other clones covering this area. A G-to-Achange causes a change of amino acid 278 from a glycine to a serine. Theproteolytic processing site Arg Arg Arg Arg Arg (black bar) immediatelyprecedes the NH₂ terminus of the mature β_(A) subunit, with theprosequences located upstream. The amino acids for the β_(A) subunitonly are numbered.

FIG. 3 is a Northern blot analysis of porcine ovarian mRNA with α, β_(A)and β_(B) subunit cDNA hybridization probes. Lanes a, b, c, d, and f arepolyA⁺ mRNA and e and g are total RNA. The position of the 28S and 18Sribosomal RNAs are shown. Lanes a, d, and e were hybridized with anα-subunit cDNA probe; lanes d, e and g with a β_(A) subunit specificprobe, and lane c with a β_(B) subunit specific probe. The α-subunitmRNA is approximately 1.5 kb, the β_(A) subunit mRNAs are approximately4.5 kb. The hybridizations shown in lanes a, b, and c were performedwith probes of approximately equal length and specific activity in orderto judge relative mRNA levels.

FIG. 4A is a comparison of the human β-TGF amino acid sequence andporcine inhibin β_(A) and β_(B) amino acid sequences. The sequences werealigned around the cysteine residues. Identical residues are boxed,while conservative changes are designated by an asterisk.

FIG. 4B compares the α-subunit sequence with the β_(A) -inhibinsequence.

FIG. 5A-C depicts the construction of a representative recombinantexpression plasmid for porcine inhibin.

FIG. 6A-B shows the nucleotide sequence and deduced amino acid sequenceof the human α-inhibin cDNA. The 355 amino acid pro- or inhibin sequenceis numbered from the hypothesized signal cleavage site. Sixteen aminoacids of the signal sequence are numbered -1 through -16. Homology withthe porcine sequence predicts a further 12 amino acid residues in thesignal sequence. In this and other figures, putative dibasic processingsites are shown by the open bars, glycosylation sites indicated bycross-hatched bars, and amino terminal mature chain processing sites aredepicted as black bars. The poly(A) additional signal sequence isunderlined. Cysteine residues are shaded.

FIG. 7A-B is a comparison of the human and porcine α-inhibin proteinsequences. Spaces are introduced to maximize the homology; positions ofnon-identity are indicated by stars. Numbering is as for the porcinesequence, which is one amino acid shorter than the human.

FIG. 8A-C shows that the nucleotide and deduced amino acid sequence ofthe human β_(A) inhibin signal sequence (residues -28 through -1) is 28amino acids with the precursor being 378 amino acids in length. Thebasic processing site is indicated by a black bar, and a potentialglycosylation site in the precursor is indicated by a cross-hatched barabove the sequence. Cysteine residues are shaded.

FIG. 9A-C illustrates the nucleotide and deduced amino acid sequence ofhuman β_(B) inhibin cDNA. The sequence commences at a cysteine residue(position 7), which lines up with the cysteine present at residue 7 inthe β_(A) sequence (see FIG. 8). The processing site for the matureβ_(B) inhibin is shown as a black bar and a potential glycosylation siteas a cross-hatched bar. Cysteine residues are shaded.

DETAILED DESCRIPTION

The polypeptides of this invention are the α and β chains of inhibin, aswell as their multimer forms (activin and inhibin), their prepro formsand their prodomains, together with glycosylation and/or amino acidsequence variants of each chain or form thereof. Inhibin (includingalleles) from human or animal sources inhibits the basal release of FSHbut not of LH from anterior pituitary cells while activin does theopposite (hereinafter referred to as "hormonally active" activin orinhibin).

Generally, amino acid sequence variants will be substantially homologouswith the relevant portion of the porcine or human α and β chainsequences set forth in FIGS. 1B, 2B, 6, 8 and 9. Substantiallyhomologous means that greater than about 70% of the primary amino acidsequence of the candidate polypeptide corresponds to the sequence of theporcine or human chain when aligned in order to maximize the number ofamino acid residue matches between the two proteins. Alignment tomaximize matches of residues includes shifting the amino and/or carboxylterminus, introducing gaps as required and/or deleting residues presentas inserts in the candidate. For example, see FIGS. 2B and 7 where theβ_(A) and β_(B) subunits for human and porcine α-inhibin sequences arealigned for maximum homology. Typically, amino acid sequence variantswill be greater than about 90% homologous with the corresponding nativesequences shown in FIGS. 1B, 2B, 6, 8 and 9.

Variants that are not hormonally-active fall within the scope of thisinvention, and include polypeptides that may or may not be substantiallyhomologous with either a mature inhibin chain or prodomain sequence, butwhich are 1) immunologically cross-reactive with antibodies raisedagainst the native counterpart or 2) capable of competing with suchnative counterpart polypeptides for cell surface receptor binding.Hormonally inactive variants are produced by the recombinant or organicsynthetic preparation of fragments, in particular the isolated α or βchains of inhibin, or by introducing amino acid sequence variations sothat the molecules no longer demonstrate hormonal activity as definedabove.

Immunological or receptor cross-reactivity means that the candidatepolypeptide is capable of competitively inhibiting the binding of thehormonally-active analogue to polyclonal antisera raised against thehormonally-active analogue. Such antisera are prepared in conventionalfashion by injecting goats or rabbits S.C. with the hormonally-activeanalogue or derivative in complete Freunds adjuvant, followed by boosterintraperitoneal or S.C. injections in incomplete Freunds.

Variants that are not hormonally active but which are capable ofcross-reacting with antisera to hormonally-active inhibin, activin, orprodomains are useful (a) as reagents in diagnostic assays for thenative analogues or their antibodies, (b) when insolubilized in accordwith known methods, as an agent for purifying anti-native analogueantibodies from antisera, and (c) as an immunogen for raising antibodiesto hormonally-active analogues.

This invention includes the pro and/or prepro sequences of the inhibin αor β chain precursors, or their immunologically or biologically activefragments, substantially free of the corresponding mature inhibinchains. These sequences for porcine and human inhibin are shown in FIGS.1B, 2B, 6, 8 and 9. The prepro sequence for the porcine α subunitprecursor is the polypeptide comprised by residues 1 to about 230, whilethe β_(A) subunit pro sequence is comprised by residues 1 to about 308.These sequences shall be referred to herein as encompassing prodomainsequences.

The α and β subunit prodomain sequences are comprised of several domainsbounded by proteolysis sites, any one of which is synthesized hereinseparately or in combination with other domains. The principal porcineβ_(A) domains fall within residues 1 to about 70 (domain I), about 70 toabout 110 (domain II), about 110 to about 180 (domain III), about 180 toabout 260 (domain IV), and about 270 to about 309 (domain V). Inparticular, the porcine β_(A) domains areGHSAAPDCPSCALATLPKDVPNSQPEMVEAV, HILNMLHLKKRPDVTQPVPKAALLNAI,LHVGKVGENGYVELEDDIG,AEMNELMEQTSEIITFAEAGRARKTLRFEISKEGSDLSVVERAEIWLFKVPKANRTRTKV SIRLFQQQ,PQGSADAGEEAEDVGFPEEKSEVLISEKVVDA,STWHIFPVSSSIQRLLDQGKSALDIRTACEQCHETGASLVLLG, andGHSAAPDCPSCALATLPKDVPNSQPEMVEAVKKHILNMLHLKKRPDVTQPVPKAALLNAI. Theporcine β_(B) domains comprise RAAHILLHAVRVSGWLNL as well as homologousβ domains having the same sequences. The porcine α domains compriseGPELDRELVLAKVRALFLDALGPPAVTGEGGDPGV andGSEPEEEDVSQAILFPATGARCGAEPAAGELAREAEEGLFTYVGRPSQHTHSRQVTSAQLWFHTGLDRQGMAAANSSGPLLDLLALSSRGPVAVPMSLGQAPPRWAVLHLAASALPLLTHPVLVLLLRCPLCSCSARPEATPFLVAHTRARPPSGGERA. A typical combination domain polypeptidewould be β_(A) domain II linked at its C-terminus to the NH₂ -terminusof β_(A) domain III. In addition, these domains are fused together bythe proteolysis sites found in the sequences shown in FIGS. 1B or 2B, by1 to 4 residues polypeptides that are resistant to hydrolysis (forexample, glutaminyl or histidyl residues), or are directly fused,whereby, in all three instances, combination domain polypeptides areproduced.

Principal human α chain prodomains are approximately residues 30-199 and1 to 29, human βA prodomains are approximately residues 1-30, 32-40,43-59, 62-80, 83-185 and 186-230 while human β_(B) prodomains areapproximately residues 1-13, 15-30, 32-59, 62-145, 148-195 and 198-241(referring to the numbering system adopted in FIGS. 6, 8 and 9,respectively). Combination prodomain polypeptides are within the scopehereof, for example, the β_(A) prodomain at about 43-80, and the β_(B)prodomains at about 1-30 and about 32-145. The preferred human α, β_(A)and β_(B) chain prodomains are about residues 1-29, about 43-80 andabout 1-30, respectively.

The intact isolated prepro or prodomain β_(A), β_(B) or α sequences arebest synthesized in recombinant cell culture. The individualsubcomponent domains are synthesized by routine methods of organicchemistry or by recombinant cell culture. They then are labelled with aradioisotope or other detectable group such as an enzyme or fluorophorein accord with known methods and used in standard competitiveimmunoassays to detect the levels of prepro or pro forms of inhibin,including individual domains, in transformants with DNA encoding suchforms or their precursors. This assay is useful in determining whetherproteolytic hydrolysis of proinhibin is occurring in the hosttransformants or their culture media. The assay also is useful indetermining whether a rate limiting step in recombinant synthesis istranslation of mRNA into the prepro forms or processing of the preproforms into mature inhibin. For example, high levels of prepro or proinhibin in cell lysates, but relatively low levels of secreted matureinhibin, would suggest that the host cell is adequately transcribing andtranslating the inhibin DNA, but is not processing the precursors at anadequate rate. Thus, in this case one would select an alternate hostcell rather than concentrating on improving the transcription ortranslation efficiency of the transforming plasmid, e.g., by selectingan alternative promoter. The prodomain sequences also are believed to beinvolved in coordinate modulation of animal physiology in reproductivecycles and fertility.

Amino acid sequence variants are any one of 1) hormonally-active, 2)cross reactive with antibodies raised against mature inhibin orprodomain α or β chain sequences, or 3) cross-reactive withinhibin/activin cell surface receptors, but are characterized by aprimary amino acid sequence that departs from the sequence of naturalinhibins or prodomain sequences. These derivatives ordinarily arepreprepared by introducing insertions, deletions or substitutions ofnucleotides into the DNA encoding the target DNA to be modified in orderto encode the variant, and thereafter expressing the DNA in recombinantcell culture. Polypeptides having up to about 100-150 residues also areconveniently prepared in vitro synthesis. Such variants arecharacterized by the predetermined nature of the variation, a featurethat sets them apart from naturally occurring allelic or interspeciesvariation. The variants may exhibit the same qualitative biologicalactivity as the naturally-occurring analogue or may act antagonisticallytowards such analogues.

While the site for introducing a sequence variation is predetermined, itis unnecessary that the mutation per se be predetermined. For example,in order to optimize the performance of mutation at a given site, randommutagenesis may be conducted at the target codon or region and theexpressed inhibin mutants screened for the optimal combination ofdesired activity. Techniques for making substitution mutations atpredetermined sites in DNA having a known sequence is well known, forexample M13 primer mutagenesis.

Mutagenesis is conducted by making amino acid insertions, usually on theorder of about from 1 to 10 amino acid residues, or deletions of aboutfrom 1 to 30 residues. Deletions or insertions preferably are made inadjacent pairs, i.e. a deletion of 2 residues or insertion of 2residues. Substitutions, deletions, insertions or any subcombination maybe combined to arrive at a final construct. Insertions include amino- orcarboxyl-terminal fusions, e.g. a hydrophobic extension added to thecarboxyl terminus. Preferably, however, only substitution mutagenesis isconducted. Obviously, the mutations in the encoding DNA must not placethe sequence out of reading frame and preferably will not createcomplementary regions that could produce secondary mRNA structure.

Not all mutations in the DNA which encode the polypeptide herein will beexpressed in the final secreted product. For example, a major class ofDNA substitution mutations are those in which a different secretoryleader or signal has been substituted for the native porcine or human αor β chain secretory leader, either by deletions within the leadersequence or by substitutions, wherein most or all of the native leaderis exchanged for a leader more likely to be recognized by the intendedhost. For example, in constructing a procaryotic expression vector theporcine or human α or β chain secretory leader is deleted in favor ofthe bacterial alkaline phosphatase or heat stable enterotoxin IIleaders, and for yeast the leader is substituted in favor of the yeastinvertase, alpha factor or acid phosphatase leaders. However, theporcine and human secretory leaders are recognized by many heterologoushigher eukaryotic cells. When the secretory leader is "recognized" bythe host, the host signal peptidase is capable of cleaving a fusion ofthe leader polypeptide fused at its C-terminus to the mature inhibin orprodomain such that mature inhibin or prodomain polypeptide is secreted.

Another major class of DNA mutants that are not expressed in final formas amino acid sequence variations are nucleotide substitutions made inthe DNA to enhance expression, primarily to avoid 5' stem and loopstructures in the transcribed mRNA (see de Boer et al., EP 75,444A) orto provide codons that are more readily transcribed by the selectedhost, e.g. the wellknown preference codons for E. coli or yeastexpression. These substitutions may or may not encode substituted aminoacid residues, but preferably do not.

Insertional and deletional amino acid sequence variants are proteins inwhich one or more amino acid residues are introduced into or removedfrom a predetermined site in the target inhibin, activin, prodomain orproform of inhibin or activin. Most commonly, insertional variants arefusions of heterologous proteins or polypeptides to the amino orcarboxyl terminus of the α or β chains, the prodomains or other inhibinderivatives. Immunogenic derivatives are made by fusing an immunogenicpolypeptide to the target sequence, e.g. a prodomain polypeptide, bysynthesis in vitro or by recombinant cell culture transformed with DNAencoding the fusion. Such immunogenic polypeptides preferably arebacterial polypeptides such as trpLE, betagalactosidase and the like,together with their immunogenic fragments. Other insertions entailinserting heterologous eukaryotic (e.g. the herpes virus gD signal) ormicrobial secretion signal or protease processing sequences upstreamfrom the NH₂ -terminus of the protein to be secreted. Deletions ofcysteine or other labile residues also may be desirable, for example inincreasing the oxidative stability of the α or β chain. Deletionalderivatives will produce α or β chain fragments. Such fragments, whenbiologically or immunologically active, are within the scope herein. Forinstance, a fragment comprising β_(B) or β_(A) residues about from 11 to45 (numbered from mature Gly₁) is to be included within the scopeherein.

Immunogenic conjugates of prodomain polypeptides, inhibin and activinare readily synthesized in recombinant cell culture as fusions withimmunogenic polypeptides, e.g. betalactamase or viral antigens such asthe herpes gD protein, or by preparation of the polypeptides in unfusedform (by recombinant or in vitro synthetic methods) followed by covalentcross-linking to an immunogenic polypeptide such as keyhole limpethemocyanin or STI using a divalent cross-linking agent. The immunogenicpolypeptides are formulated with a vaccine adjuvant, e.g. alum orFreunds. Methods for preparing proteins in adjuvants and forcross-linking are well-known per se and would be employed by one skilledin the art, as are methods for vaccinating animals. The immunogenicconjugates are useful in preparing antibodies to the prodomain regionfor use in monitoring inhibin manufacture or for in vivo vaccinationwith the objective of raising antibodies capable of modulating animalphysiology in reproductive cycles and fertility. Typically, theprodomain or its immunogen is administered in varied doses to fertilelaboratory animals or swine and the reproductive cycles and fertility ofthe animals monitored, together with assays of serum levels ofanti-immunogen or prodomain by routine competitive or sandwichimmunoassay.

Substitution derivatives are produced by mutating the DNA in a targetcodon, so that thereafter a different amino acid is encoded by thecodon, with no concomitant change in the number of residues present inthe molecule expressed from the mutated DNA. Substitutions or deletionsare useful for example in increasing the stability of the proteinsherein by eliminating proteolysis sites, wherein residues aresubstituted within or adjacent to the sites or are deleted from thesites, or by introducing additional disulfide bonds through thesubstitution of cysteine for other residues. Substitutions are usefulfor facilitating the synthesis or recovery of mature or prodomain α or βchains. For example, methionine residues within the mature inhibinsequences are substituted or deleted, prepro sequences deleted,methionine is inserted at the -1 site immediately NH₂ terminal to themature NH₂ terminal residue and another sequence inserted N-terminal tothe exogenous methionine. The inhibin derivative in this case isexpressed as a fusion having an intermediate methionyl residue, which inturn is cleaved at this residue by cyanogen bromide in accordance withknown practice. The mature inhibin derivative released from the fusionis recovered.

Exemplary porcine inhibin derivatives are [Asn₂₆₆ →Gln[Inhα (to removethe putative glycosylation site), [Cys₃₂₅ or Cys₃₄₄ →Δ]Inhα, [Cys₃₆₁ orCys₃₆₃ →Δ]Inhα, [Lys₃₂₁ or Lys₃₂₂ →Δ]Inhβ_(A) or [Lys₃₃₂ →His orSer]Inhβ_(A) (to inactivate a potential proteolysis site), [Lys₃₁₅ →Arg;Val₃₁₆ →Thr] Inhβ_(A) (to create a β_(A) /β_(B) hybrid), [Cys₃₈₈ orCys₃₉₀ →Δ]Inhβ_(A), [Lys₄₁₁ →Gln]Inhβ_(A), [Arg₃₁₅ →Lys, Val₃₁₆→Thr]Inhβ_(B) (to create a β_(B) /β_(A) hybrid), [Cys₃₁₉ or Cys₃₂→Δ]Inhβ_(B) [Pro₃₈₁ Gly₃₈₂ →Pro Phe Gly]Inhβ_(B), and [Arg₃₉₅→Gln]Inhβ_(B), wherein Inh is an abbreviation for inhibin and theresidue numbers for Inhβ_(B) are those used for the correspondingInhβ_(A) residue (see FIG. 2B).

The hβ_(A) amino acid positions which are principal candidates formutational substitution or deletion (or adjacent to which residues maybe inserted) include residues 293-297, 364-376 and 387-398 (FIG. 8).Preferably, the proline, cysteine and glycine residues within thesesequences are not modified. Candidates having greater potency thaninhibin or activin, or which serve as inhibin or activin antagonists,are identified by a screening assay wherein the candidate is dilutedinto solutions containing constant amounts of inhibin or activin and thecompositions are assayed in the rat pituitary cell assay. Candidateswhich neither antagonize or agonize inhibin or activin are screened forutility in immunoassays for inhibin or activin by measuring competitiveimmunodisplacement of labelled inhibin or activin of the native hormonesfrom polyclonal antibody directed against the native hormones. Exemplarycontemplated sequence variants of hβ_(A) include Phe₃₀₂ →Ile or Leu;Gln₂₉₇ →Asp or Lys; Trp₃₀₇ →Tyr or Phe; Trp₃₁₀ →Tyr or Phe; Ile₃₁₁ →Pheor Val; Tyr₃₁₇ →Trp or Thr; His₃₁₈ →Lys; Ala₃₁₉ →Ser; Asn₃₂₀ →Gln, Tyror His; Tyr₃₂₁ →Thr or Asp, Phe₃₄₀ →Tyr (a TGF-β/β_(A) intrachainhybrid); His₃₅₃ →Asp; His₃₅₃ →Lys (a β_(A) /β_(B) hybrid); Phe₃₅₆ →Tyr;Val₃₆₄

→Phe; Val₃₆₄ →Leu; Tyr₃₇₅ →Thr; Tyr₃₇₆ →Trp; Asn₃₈₉ →Gln, His or Lys;Ile₃₉₁ →Leu or Thr; Met₃₉₀ →Leu or Ser; Val₃₉₂ →Phe, Glu, Thr or Ile.Comparable modifications are made in the human β_(B) chain. For example,hβ_(A) contains a phenylalanyl residue at position 302, and hβ_(B) alsocontains a phenylalanyl residue at a homologous position (264, FIG. 9),when aligned in the same fashion as is shown for porcine β_(B) in FIG.4A. Thus, since the Phe₃₀₂ residue of β_(A) is described above assubstituted by isoleucinyl or leucinyl, the Phe₂₆₄ of β_(B) issubstituted with the same residues.

A factor in establishing the identity of a polypeptide as inhibinactivin or an inhibin variant is the ability of antisera which arecapable of substantially neutralizing the hormonal activity of matureinhibin or activin to also substantially neutralize the hormonalactivity of the polypeptide in question. However it will be recognizedthat immunological identity and hormonal activity are not necessarilycoextensive. For example, a neutralizing antibody for inhibin may notbind a candidate protein because the neutralizing antibody happens tonot be directed to specifically bind a site on inhibin that is criticalto its activity. Instead, the antibody may bind an innocuous region andexert its neutralizing effect by steric hindrance. Therefore a candidateprotein mutated in this innocuous region might no longer bind theneutralizing antibody, but it would nonetheless be inhibin in terms ofsubstantial homology and biological activity.

It is important to observe that characteristics such as molecularweight, isoelectric point and the like for a native or wild type matureinhibin or activin obtained from follicular fluid or other tissuesources are descriptive only for the native form. Variants contemplatedby the foregoing definition will include other polypeptides which willnot exhibit all of the characteristics of native analogue. For example,inhibin derivatives like the insertion mutants, deletion mutants, orfusion proteins described above will bring inhibin outside of themolecular weight established for the corresponding native inhibinbecause fusion proteins with mature inhibin or proinhibin itself as wellas insertion mutants will have a greater molecular weight than native,mature inhibin. On the other hand, deletion mutants of native, matureinhibin will have a lower molecular weight. Finally, post-translationalprocessing or preproinhibin chains in heterologous cell lines may not beaccomplished with the fidelity exercised by the homologous host cell,thereby resulting in some variation in the amino termini of the α and/orβ chains. This variation may be encountered as residual prosequenceremaining with the mature protein, or the loss of several matureresidues that are cleaved off with the prosequence. The same is truewith processing of the preprotein in heterologous recombinant cells.

Covalent modifications of inhibin, activin or prodomains are includedwithin the scope hereof and include covalent or aggregative conjugateswith other chemical moieties. Covalent derivatives are prepared bylinkage of functionalities to groups which are found in the inhibinamino acid side chains or at the N- or C-termini, by means known in theart. For example, these derivatives will include: aliphatic esters oramides of the carboxyl terminus or residues containing carboxyl sidechains, e.g., aspartyl residues; O-acyl derivatives of hydroxylgroupcontaining residues such as seryl or alanyl; and N-acyl derivativesof the amino terminal amino acid or amino-group containing residues,e.g. lysine or arginine. The acyl group is selected from the group ofalkyl moieties (including C3 to C10 normal alkyl), thereby formingalkanoyl species, and carbocyclic or heterocyclic compounds, therebyforming aroyl species. The reactive groups preferably are difunctionalcompounds known per se for use in cross-linking proteins to insolublematrices through reactive side groups, e.g. m-maleimidobenzoyl-N-hydroxysuccinimide ester. Preferred derivatization sites are at histidineresidues.

Covalent or aggregative derivatives of mature inhibin, activin orprodomain sequences are useful as reagents in immunoassay or foraffinity purification procedures. For example, inhibin or prodomain isinsolubilized by covalent bonding to cyanogen bromide-activatedSepharose by methods known per se or adsorbed to polyolefin surfaces(with or without glutaraldehyde cross-linking) for use in the assay orpurification of antiinhibin or anti-prodomain antibodies or cell surfacereceptors. Inhibin or a prodomain sequence also is labelled with adetectable group, e.g., radioiodinated by the chloramine T procedure,covalently bound to rare earth chelates or conjugated to anotherfluorescent moiety for use in diagnostic assays, especially fordiagnosis of inhibin or prodomain levels in biological samples bycompetitive-type immunoassays.

DNA which encodes the complete α and β chains of inhibin/activin isobtained by chemical synthesis, by screening reverse transcripts of mRNAfrom ovary, or by screening genomic libraries from any cell. It may bemore efficient to simply synthesize portions of the DNA desired sincescreening is required to identify DNA in cDNA or genomic libraries thatencode the α and β chains. Synthesis also is advantageous because uniquerestriction sites can be introduced at the time of preparing the DNA,thereby facilitating the use of the gene in vectors containingrestriction sites otherwise not present in the native sequence, andsteps can be taken to enhance translational efficiency as discussedabove, without the need to further modify the DNA as by mutagenesis orthe like. cDNA encoding the α or β chains is free of untranslatedintervening sequences (introns) as well as free of flanking DNA encodingother proteins homologous to their source.

DNA encoding the α and β chains is obtained from other sources thanporcine or human by (a) obtaining a cDNA library from the ovary of thetarget animal, (b) conducting Southern analysis with labelled DNAencoding porcine or human α and β chains or fragments thereof(generally, greater than 100 bp) in order to detect clones in the cDNAlibrary that contain homologous sequences, (c) analyzing the clones byrestriction enzyme analysis and nucleic acid sequencing so as toidentify full-length clones and, if full length clones are not presentin the library, recovering appropriate fragments from the various clonesand ligating them at restriction sites common to the clones to assemblea clone encoding the full-length molecule. As shown infra, any sequencesmissing from the library can be obtained by the 3' extension on ovarianmRNA of synthetic oligodeoxynucleotides complementary to cDNA identifiedby screening the library, or homologous sequences are supplied fromknown animal cDNAs. This is particularly useful in constructing pre orprepro inhibin sequence to facilitate processing of preproinhibin tomature inhibin from the desired species.

Porcine and human ovarian cDNA libraries initially were probed for DNAencoding inhibin sequences using labelled oligonucleotides whosesequence was based on the partial amino acid sequence determined fromanalysis of purified porcine inhibin or, in the case of human cDNA,porcine probes. However, once having described cDNA encoding human andporcine inhibin and prodomains, one skilled in the art would realizethat precisely hybridizing probes can be prepared from the describedsequences in order to readily obtain the remainder of the desired humanor porcine gene.

Nucleotide sequence analyses of identified porcine and human cDNA clonesrevealed the structures of the biosynthetic precursors of both forms ofinhibin. Interestingly, the two inhibin chains are not derived from asingle processed precursor. Instead, the two chains are translated fromseparate mRNAs and then assembled into the disulfide crosslinkedtwo-chain molecule.

FIGS. 1B and 2B and 6, 8 and 9 depict the DNA encoding the polypeptidechains constituting porcine and human preproinhibin and preproactivin.Obviously, degenerate codons may be substituted for those disclosed inthese figures where the same amino acid is encoded. The DNA of FIGS. 1B,2B, 6, 8 and 9 is mutated in order to encode the amino acid variants ofthe α and β chains described above. In particular, the prepro sequencesare deleted and a start codon is inserted immediately 5' to the maturechain in question so that the chain is expressed directly in recombinantculture. The DNA also is labelled, e.g. with radioactive phosphorous,and used to screen ovarian cDNA libraries from other species to identifyα or β chain encoding DNA from such other species as is generallydescribed above.

Covalent labelling of this DNA is accomplished with a detectablesubstance such as a fluorescent group, a radioactive atom or achemiluminescent group by methods known per se. The labelled DNA is thenused in conventional hybridization assays. Such assays are employed inidentifying vectors and transformants as described in the examplesinfra, or for in vitro diagnosis such as detection of mRNA in tissues.

Lengthy sequences desirably are synthesized in host cells transformedwith vectors containing DNA encoding them, e.g. inhibin or prodomainsequence. Vectors are used to amplify the DNA which encodes the chains,either in order to prepare quantities of DNA for further processing(cloning vectors) or for expression of the chains (expression vectors).An expression vector is a replicable DNA construct in which a DNAsequence encoding an α or β chain is operably linked to suitable controlsequences capable of effecting their expression in a suitable host.Cloning vectors need not contain expression control sequences. Suchcontrol sequences include a transcriptional promoter, an optionaloperator sequence to control transcription, a sequence encoding suitablemRNA ribosomal binding sites (for prokaryotic expression), and sequenceswhich control termination of transcription and translation. The vectorshould include a selection gene to facilitate the stable expression ofthe desired polypeptide and/or to identify transformants. However, theselection gene for maintaining α and/or β chain expression can besupplied by a separate vector in cotransformation systems usingeukaryotic host cells.

Vectors comprise plasmids, viruses (including phage), and integratableDNA fragments i.e., fragments that are integratable into the host genomeby recombination. The vectors described herein for use in eukaryoticcell expression of inhibin α and/or β chains contain plasmid sequencesfor cloning in microbes, where the plasmid replicates autonomously fromthe host genome, but the DNA is believed to integrate into theeukaryotic host cell genome upon transformation. Similarly, bacillusvectors that genomically integrate by homologous recombination inbacillus also are useful. However, all other forms of vectors whichserve an equivalent function and which are, or become, known in the artare suitable for use herein.

Suitable vectors generally will contain replicon (origins ofreplication, for use in non-integrative vectors) and control sequenceswhich are derived from species compatible with the intended expressionhost. Transformed host cells are cells which have been transformed ortransfected with vectors containing inhibin α and/or β chain encodingDNA. Transformed host cells contain cloned DNA and, when transformedwith an expression vector, also express the α and/or β chains. Theexpressed polypeptides will be deposited intracellularly or secretedinto either the periplasmic space or the culture supernatant, dependingupon the host cell selected and the presence of suitable processingsignals in the expressed protein, e.g. homologous or heterologous signalsequences.

DNA regions are operably linked when they are functionally related toeach other. For example, DNA for a presequence or secretory leader isoperably linked to DNA for a polypeptide if it is expressed as apreprotein which participates in the secretion of the polypeptide; apromoter is operably linked to a coding sequence if it controls thetranscription of the sequence; or a ribosome binding site is operablylinked to a coding sequence if it is positioned so as to permittranslation. Generally, operably linked means that the DNA sequencebeing linked are contiguous and, in the case of secretory leaders,contiguous and in reading phase.

Suitable host cells are prokaryotes, yeast or higher eukaryotic cells.Prokaryotes include gram negative or gram positive organisms, forexample E. coli or Bacilli. Higher eukaryotic cells include establishedcell lines of mammalian origin as described below. A preferred host cellis E. coli 294 (ATCC 31,446) although other prokaryotes such as E. coliB, E. coli X1776 (ATCC 31,537), E. coli W3110 (ATCC 27,325), pseudomonasspecies, or Serratia Marcesans are suitable.

Expression vectors for host cells ordinarily include an origin ofreplication (where extrachromosomal amplification is desired, as incloning, the origin will be a bacterial origin), a promoter locatedupstream from the inhibin coding sequences, together with a ribosomebinding site (the ribosome binding or Shine-Dalgarno sequence is onlyneeded for prokaryotic expression), RNA splice site (if the inhibin DNAcontains genomic DNA containing one or more introns), a polyadenylationsite, and a transcriptional termination sequence. As noted, the skilledartisan will appreciate that certain of these sequences are not requiredfor expression in certain hosts. An expression vector for use withmicrobes need only contain an origin of replication recognized by theintended host, a promoter which will function in the host and aphenotypic selection gene, for example a gene encoding proteinsconferring antibiotic resistance or supplying an auxotrophicrequirement. Inhibin DNA is typically cloned in E. coli using pBR322, aplasmid derived from an E. coli species (Bolivar, et al., 1977, "Gene"2: 95). pBR322 contains genes for ampicillin and tetracycline resistanceand thus provides easy means for identifying transformed cells.

Expression vectors, unlike cloning vectors, must contain a promoterwhich is recognized by the host organism. This is generally a promoterhomologous to the intended host. Promoters most commonly used inrecombinant DNA constructions include the β-lactamase (penicillinase)and lactose promoter systems (Chang et al., 1978, "Nature", 275: 615;and Goeddel et al., 1979, "Nature" 281: 544), a tryptophan (trp)promoter system (Goeddel et al., 1980, "Nucleic Acids Res." 8: 4057 andEPO Appl. Publ. No. 36,776) and the tack promoter [H. De Boer et al.,1983, "Proc. Nat'l. Acad. Sci. U.S.A." 80: 21-25]. While these are themost commonly used, other known microbial promoters are suitable.Details concerning their nucleotide sequences have been published,enabling a skilled worker operably to ligate them to DNA encodinginhibin in plasmid vectors (Siebenlist et al., 1980, "Cell" 20: 269) andthe DNA encoding inhibin or its derivative. Promoters for use inprokaryotic expression systems also will contain a Shine-Dalgarno (S.D.)sequence operably linked to the DNA encoding the inhibin, i.e., the S.D.sequence is positioned so as to facilitate translation. Generally, thismeans that the promoter and S.D. sequences located upstream from thesecond codon of a bacterial structural gene are substituted for thesequences of prepro inhibin located 5' to the mature α and/or β chains.

In addition to prokaryotes, eukaryotic microbes such as yeast culturesare transformed with inhibin-encoding vectors. Saccharomyces cerevisiae,or common baker's yeast, is the most commonly used among lowereukaryotic host microorganisms. However, a number of other strains arecommonly available and useful herein. Yeast vectors generally willcontain an origin of replication from the 2 micron yeast plasmid or anautonomously replicating sequence (ARS), a promoter, DNA encoding the αand/or β chain, sequences for polyadenylation and transcriptiontermination, and a selection gene. A suitable plasmid for expression inyeast is YRp7, (Stinchcomb et al., 1979, "Nature", 282: 39; Kingsman etal., 1979, "Gene", 7: 141; Tschemper et al., 1980, "Gene", 10:157). Thisplasmid already contains the trpl gene which provides a selection markerfor a mutant strain of yeast lacking the ability to grow in tryptophan,for example ATCC No. 44076 or PEP4-1 (Jones, 1977, "Genetics", 85: 12).The presence of the trpl lesion in the yeast host cell genome thenprovides an effective environment for detecting transformation by growthin the absence of tryptophan.

Suitable promoting sequences in yeast vectors include the promoters formetallothionein, 3-phosphoglycerate kinase (Hitzeman et al., 1980, "J.Biol. Chem.", 255: 2073) or other glycolytic enzymes (Hess et al., 1968,"J. Adv. Enzyme Reg.", 7: 149; and Holland et al., 1978, "Biochemistry",17: 4900), such as enolase, glyceraldehyde-3-phosphate dehydrogenase,hexokinase, pyruvate decarboxylase, phosphofructokinase,glucose-6-phosphate isomerase, 3-phosphoglycerate mutase, pyruvate,kinase, triosephosphate isomerase, phosphoglucose isomerase, andglucokinase. Suitable vectors and promoters for use in yeast expressionare further described in R. Hitzeman et al., EP 73,657A.

Other yeast promoters, which have the additional advantage oftranscription controlled by growth conditions, are the promoter regionfor alcohol dehydrogenase 2, isocytochrome C, acid phosphatase,degradative enzymes associated with nitrogen metabolism, and theaforementioned metallothionein and glyceraldehyde-3- phosphatedehydrogenase, as well as enzymes responsible for maltose and galactoseutilization. In constructing suitable expression plasmids, thetermination sequences associated with these genes are also ligated intothe expression vector 3' of the inhibin or derivative coding sequencesto provide termination and polyadenylation of the mRNA.

Cultures of cells derived from multicellular organisms are the preferredhost cells herein because it is believed that expression of hormonallyactive inhibin or activin will only occur in such cells, with microbialexpression resulting at most only in immunological cross-reactivity. Inprinciple, any higher eukaryotic cell culture is workable, whether fromvertebrate or invertebrate culture. Propagation of vertebrate cells inculture per se has become a routine procedure in recent years ([TissueCulture, Academic Press, Kruse and Patterson, editors (1973)].

Suitable host cells for expressing α or β chains in higher eukaryotesinclude: monkey kidney CVI line transformed by SV40 (COS-7, ATCC CRL1651); baby hamster kidney cells (BHK, ATCC CRL 10); Chinese hamsterovary-cells-DHFR (described by Urlaub and Chasin, PNAS (USA) 77: 4216,[1980]); mouse sertoli cells (TM4, Mather, J. P., Biol. Reprod. 23:243-251 [1980]); monkey kidney cells (CVI ATCC CCL 70); African greenmonkey kidney cells (VERO76, ATCC CRL-1587); human cervical carcinomacells (HELA, ATCC CCL 2); canine kidney cells (MDCK, ATCC CCL 34);buffalo rat liver cells (BRL 3A, ATCC CRL 1442); human lung cells (W138,ATCC CCL 75); human liver cells (Hep G2, HB 8065); mouse mammary tumor(MMT 060652, ATCC CCL 51); rat hepatoma cells (HTC, M1, 54, Baumann, M.,et al., J. Cell. Biol. 85 1-8 [1980]) and TRI cells (Mather, J. P. etal., Annals N.Y. Acad. Sci. 383: 44-68 [1982]).

The transcriptional and translational control sequences in vertebratecell expression vectors preferably are provided from viral sources. Forexample, commonly used promoters are derived from polyoma, Adenovirus 2,and most preferably Simian Virus 40 (SV40). The early and late promotersof SV40 are particularly useful because both are obtained easily fromthe virus as a fragment which also contains the SV40 viral origin ofreplication (Fiers et al., 1978, "Nature", 273: 113). Smaller or largerSV40 fragments may also be used, provided the approximately 250 bpsequence extending from the Hind III site toward the Bgl I site locatedin the viral origin of replication is included. Further, it is alsopossible to utilize the genomic promoters, control and/or signalsequences normally associated with the α or βchains, provided suchcontrol sequences are compatible with and recognized by the host cell.

An origin of replication may be provided either by construction of thevector to include an exogenous origin, such as may be obtained from SV40or other viral (e.g. Polyoma, Adenovirus, VSV, or BFV) source, or may beprovided by the host cell chromosomal replication mechanism. If thevector is integrated into the host cell chromosome, the latter is oftensufficient.

Rather than using vectors which contain viral origins of replication,mammalian cells are cotransformed with DNA encoding a selectable markerand DNA encoding the α and/or β chains. An example of a suitableselectable marker is dihydrofolate reductase (DHFR) or thymidine kinase.Such markers are proteins, generally enzymes that enable theidentification of transformant cells, i.e., cells which has beencompetent to take up exogenous DNA. Generally, identification is bysurvival of transformants in culture medium that is toxic tountransformed cells or from which the cells cannot obtain a criticalnutrient without having taken up the marker protein.

In selecting a preferred host mammalian cell for transfection by vectorswhich comprise DNA sequences encoding both inhibin and DHFR, it isappropriate to select the host according to the type of DHFR proteinemployed. If wild type DHFR protein is employed, it is preferable toselect a host cell which is deficient in DHFR thus permitting the use ofthe DHFR coding sequence as a marker for successful transfection inselective medium which lacks hypoxanthine, glycine, and thymidine(hgt⁻). An appropriate host cell in this case is the Chinese hamsterovary (CHO) cell line deficient in DHFR activity, prepared andpropagated as described by Urlaub and Chasin, 1980, "Proc. Nat'l. Acad.Sci." (USA) 77: 4216.

On the other hand, if DNA encoding DHFR protein with low bindingaffinity for methotrexate (MTX) is used as the controlling sequence, itis not necessary to use DHFR resistant cells. Because the mutant DHFR isresistant to MTX, MTX containing media can be used as a means ofselection provided that the host cells are themselves MTX sensitive.Most eukaryotic cells which are capable of absorbing MTX appear to themethotrexate sensitive. One such useful cell line is a CHO line, CHO-KI(ATCC No. CCL 61). Preferably, transformants are first selected forneomycin resistance (the transfection is conducted together with DNAencoding the neomycin resistance gene), followed by MTX amplification ofthe α and/or β chain expression as the case may be. See Kim et al.,"Cell" 42: 129-138 (1985) and EP 160,457A.

Other methods suitable for adaptation to the synthesis of α and/or βchains in recombinant vertebrate cell culture are described in M-J.Gething et al., "Nature" 293: 620-625 (1981); N. Mantei et al., "Nature"281:40-46; and A. Levinson et a., EP 117,060A and 117, 058A.

The inhibin α chain is expressed in recombinant cell culture with orwithout either of the β-chain molecules. Similarly, host cells aretransformed with DNA encoding either or both of the mature β-chains.Based on analogy to TGF-β, the mature β-chains are capable of forminghomodimers or β_(A) /β_(B) heterodimers upon expression in recombinantculture. These structures are not inhibin and will be referred to hereinas β-chain dimers or activin. These are useful in the preparation ofactive inhibin, serving as sources of the β-chain, or are used as gelelectrophoresis standards to detect the diversion into β-chain dimers ofβ-chains synthesized in α and β chain cotransformants. As will be seenin Example 4, this is not a hypothetical problem. Of course, the dimersalso are useful in modulating reproduction as noted above.

β-chain hetero or homodimers are separated by in vitro unfolding of theindividual chains followed by oxidative disulfide bond formation withthe α-chain in accord with processes generally known per se. Preferably,however, in preparing mature inhibin the recombinant host is transformedwith DNA encoding both the α and either of the β-chains. The intacthormonally active molecule is then assembled by the host cell in vivo,and it is thus unnecessary to combine the two chains by in vitroprocessing. The DNA encoding the α and β-chains is preferably located onthe same vector, and under the control of the same promoter, but this isnot essential.

Certain β-chain amino acid sequence variants identified in the screeningprocedure will not bind to pituitary cell surface receptors nor as aconsequence will they exhibit hormonal activity. Such variants, whenexpressed as homodimers in recombinant cell culture, are useful inimmunoassays for activin when they bear immunological epitopescross-reactive with the native β-chain. In addition, such variants arecoexpressed with DNA encoding hormonally active β-chain to yield ahybrid bearing native and variant β-chain. In this case the variantserves to stabilize the structure of the native β-chain. This form ofβ-chain heterodimer is useful, like the homodimer, in immunoassays foractivin. It also may function as an activin antagonist.

The activin/inhibin β-chains also are coexpressed with TGF-β in order toproduce β-chain/TGF-β hybrids. Vectors and methods for the expression ofTGF-β are known. For example, see Derynck et al., Human TransformingGrowth Factor-β Complementary DNA Sequence and Expression in Normal andTransformed Cells "Nature" 316: 701-705 (1985). Cotransformation ofmammalian host cells by vectors bearing the TGF-β gene as described byDerynck et al. together with the β_(A) or β_(B) chains ofactivin/inhibin will result in secretion of a proportion ofβ-chain/TGF-β hybrid dimers. This hybrid is useful in preparingTGF-β/β-chain immunogens or in immunoassays.

Inhibin, activin or prodomain sequences are recovered from transformedcells in accord with per se known procedures. When a polypeptide isexpressed in recombinant bacteria as a refractile body, the desiredpolypeptide is recovered and refolded by conventional methods.Alternatively, the culture supernatants from transformed cells thatsecrete activin or inhibin, preferably mammalian cells, are simplyseparated from the cells by centrifugation. Then the inhibin generallyis purified by successive purification procedures that includeheparin-Sepharose affinity chromatography, gel filtration and at leastone and preferably several RP-HPLC (reverse phase high pressure liquidchromatography) steps using different conditions in the stationary phaseand/or mobile phase. Prodomain sequences produced by in vitro synthesiswill be purified by conventional methods.

The prodomain polypeptides that are preferred for use herein arerecovered from the culture media of recombinant cells transformed tosynthesize the α and/or β chains as appropriate for the desiredprodomain. Specifically, they are recovered by separating the culturemedium polypeptides on native electrophoresis gel, excising bands havingthe predicted molecular weight and thereafter purifying the elutedpolypeptides further, for example by FPLC or HPLC, followed by aminoacid sequence determination for the substantially homogeneous separatedpolypeptides. Purified prodomain polypeptides then are used to raiseantibodies, e.g., in rabbits, which when used in immunoaffinitypurification will simplify the recovery of the prodomains.

In the preferred procedure for isolating porcine hormonally activeinhibin, clarified transformant culture supernatant or cell lysate isfirst purified by heparin-Sepharose affinity chromatography, next by gelfiltration on Sephacryl S-200 gel and then with four successive RP-HPLCsusing different mobile phase gradients and/or derivatized silicasupports. Preferably, stationary phases having relatively lowhydrophobicity are used, with C3-C8 columns being preferred and C3-C5and phenyl columns being particularly preferred. Solute specificity ofthe mobile phase is preferably adjusted by varying the concentration ofan organic component, particularly acetonitrile. Although a singleRP-HPLC fractionation significantly increases the purity relative to thegel-filtrated material, two or more, and preferably four, RP-HPLCpurifications are generally performed subsequent to successive treatmentby heparin-Sepharose chromatography and gel filtration. This method hasbeen found to be adaptable to the purification of human inhibin fromrecombinant cell culture as well.

The first step of the purification is heparin-Sepharose affinitychromatography, in which the protein is adsorbed to the Sepharose-boundheparin moieties under application conditions, and the adsorbed inhibinmaterial is recovered by 1M NaCl elution. This step greatly expeditesthe purification procedure for crude extracts because it allows arelatively large volume of a crude extract to be processed fairlyrapidly while recovering an amount of protein exhibiting total inhibinactivity equal to at least 90% of that of the crude extract.

For the detection of inhibin activity in the various column fractions,aliquots ranging from 0.01% to 0.1% by volume are removed, and afteradding 100 μg human serum albumin in 100 μl water, the solvents wereevaporated in a Speed-Vac concentrator (Savant, Hicksville, N.Y.). Theresidue was redissolved in 3 ml 1% fetal bovine serum in HDMEM, filteredthrough a Millex-GS 0.22 μm filter (Millipore Corp., Bedford, Mass.) andassayed in duplicate. To speed up the bioassays during the purificationprocess, only basal inhibition of FSH secretion exerted by the inhibinactivity is determined and plotted in the region where the inhibinproteins were expected to migrate in the chromatograms.

To perform the heparin-Sepharose affinity chromatography, cell debris isspun down in a Beckman J2-21 centrifuge (Beckman Instruments, Inc., PaloAlto, Calif.) using a JA20 rotor at 10,000 rpm for 30 minutes. One halfof the supernatant is diluted to 10 times its volume by the addition of0.01M Tris-HCl containing 0.1M NaCl, pH 7, in an Erlenmeyer flask andpumped simultaneously via silastic tubes (0.76 mm ID) intoheparin-Sepharose (Pharmacia Fine Chemicals, Piscataway, N.J.) columns(3.5×9 cm) by two Rabbit 4-channel peristaltic pumps (Rainin InstrumentCo., Inc., Emeryville, Calif.) at 40 ml/hr per column. After all thefluid has been pumped through the heparin-Sepharose, the eight columnsare washed simultaneously with 0.01M Tris-HCl, pH 7, containing 0.1MNaCl in the same manner. The adsorbed proteins with inhibin activity areremoved by washing the eight columns simultaneously with 0.01M Tris-HClcontaining 1M NaCl, pH 7, as above, and the wash is collected intofractions. The inhibin activity is monitored by the in vitro bioassaydescribed above. The columns are regenerated by further washing with 2MNaCl in 0.01M Tris-HCl, pH 7, and re-equilibrated with 0.01M Tris-HClcontaining 0.1M NaCl for purification of remaining extract.

Next, the material is fractionated by gel filtration to separateproteins generally according to their molecular weights. The fractionshaving inhibin activity extracted by the heparin-Sepharose columns arepooled and dialyzed overnight to remove NaCl in a 28.6 mm cylinderdiameter Spectrapor No. 3 membrane tubing with M_(r) cutoff at 3,500(Spectrum Medical Industries, Inc., Los Angeles, Calif.) against 30%acetic acid. The retained fluid is centrifuged, as above, to remove awhite precipitate, and the supernatant is divided into equal portionsfor applying to 5×100 cm Sephacryl S-200 superfine columns (PharmaciaFine Chemicals, Piscataway, N.J.). Each column is eluted with 30% aceticacid at 20 ml for 22 min., and the column fractions are monitored by UVabsorption at 280 nm and by bioassay.

The bioassay-positive protein from the S-200 columns is pooled andlyophilized. The lyophilized material is dissolved in 0.2N acetic acid(1 ml/ml) and filtered through a Millex-HA 0.45 μm filter (MilliporeCorp., Bedford, Mass.). The filtrate is applied directly onto a 1×25 cmVydac 5-μm particle-size C4 column (The Separations Group Hesperia,Calif.) and developed with a gradient of TEAP buffer. In the TEAPsystem, buffer A consists of 0.25N triethylammonium phosphate pH 3, andbuffer B is 80% acetonitrile in buffer A. After all the filtrate hadbeen loaded, the column is washed with the aqueous buffer A until the UVabsorption reached baseline. The fractions exhibiting inhibin activityare separated in a Beckman 332 gradient liquid chromatography system(Beckman Instruments, Inc., Berkeley, Calif.) equipped with aSpectroflow 757 UV detector (Kratos Analytical Instruments, Ramsey,N.J.), a Soltec 220 recorder (Soltec Corp., Sun Valley, Calif.) and aRedirac 2112 fraction collector (LKB Instruments, Inc., Gathersburg,Md.). Zones of inhibin activity are detected by bioassay.

Inhibin protein containing the β_(B) chain is further purified free ofinhibin containing the β_(A) species, if desired, by two more RP-HPLCsteps. The first step uses a 1×25 cm Vydac 5-μm-particle-size C4 columnand a trifluoroacetic acid (TFA) buffer system and the second stepemploys a 1×25 cm Vydac 5-μm-particle-size Phenyl column and the TEAPbuffer system. In the TFA system, buffer A contains 1 ml trifluoroaceticacid in 999 ml water and buffer B is 1 ml trifluoroacetic acid in 199 mlwater and 800 ml acetonitrile. The two inhibin species elute separately.Inhibin accumulated from a few batches was concentrated by RP-HPLC usinga 0.46×25 cm Aquapore RF-300 10 μm-particle-size column (Brownlee Labs.,Santa Clara, Calif.) and the TFA buffer system. Ordinarily, however,this purification step will not be used with cell culture supernatantsfrom transformants with DNA encoding only the β_(A) or β_(B) chains.

Inhibin, activin, prodomain sequences or their variants are administeredin the form of pharmaceutically acceptable nontoxic salts, such as acidaddition salts or metal complexes, e.g., with zinc, iron or the like(which are considered as salts for purposes of this application).Illustrative of such acid addition salts are hydrochloride,hydrobromide, sulphate, phosphate, maleate, acetate, citrate, benzoate,succinate, malate, ascorbate, tartrate and the like. Intravenousadministration in isotonic saline, phosphate buffer solutions or thelike is suitable.

The polypeptide herein should be administered under the guidance of aphysician, and pharmaceutical compositions will usually contain aneffective amount of the peptide in conjunction with a conventional,pharmaceutically-acceptable carrier. The dosage will vary depending uponthe specific purpose for which the protein is being administered, anddosage levels in the range of about 0.1 to about 1 milligrams per Kg. ofbody weight may be used when inhibin is administered on a regular basisas a male contraceptive.

Inhibin, activin, prodomain sequences or their variants desirably areadministered from an implantable or skin-adhesive sustained-releasearticle. Examples of suitable systems include copolymers of L-glutamicacid and gamma ethyl-L-glutamate (U. Sidman et al., 1983, "Biopolymers"22(1): 547-556), poly (2hydroxyethyl-methacrylate) (R. Langer et al.,1981, "J. Biomed. Mater. Res." 15: 167-277 and R. Langer, 1982, "Chem.Tech." 12: 98-105), ethylene vinyl acetate (R. Langer et al., Id.), orpoly-D(-)-3- hydroxybutyric acid (EP 133,988A). Such articles areimplanted subcutaneously or are placed into contact with the skin ormucous membranes.

In order to simplify the Examples certain frequently occurring methodswill be referenced by shorthand phrases.

Plasmids are designated by a low case p preceded and/or followed bycapital letters and/or numbers. The starting plasmids herein arecommercially available, are publicly available on an unrestricted basis,or can be constructed from publicly available plasmids or DNA in accordwith published procedures. In addition, other equivalent plasmids areknown in the art and will be apparent to the ordinary artisan.

"Digestion" of DNA refers to catalytic cleavage of the DNA with anenzyme that acts only at certain locations in the DNA. Such enzymes arecalled restriction enzymes, and the sites for which each is specific iscalled a restriction site. "Partial" digestion refers to incompletedigestion by a restriction enzyme, i.e., conditions are chosen thatresult in cleavage of some but not all of the sites for a givenrestriction endonuclease in a DNA substrate. The various restrictionenzymes used herein are commercially available and their reactionconditions, cofactors and other requirements as established by theenzyme suppliers were used. Restriction enzymes commonly are designatedby abbreviations composed of a capital letter followed by other lettersand then, generally, a number representing the microorganism from whicheach restriction enzyme originally was obtained. In general, about 1 μgof plasmid or DNA fragment is used with about 1 unit of enzyme in about20 μl of buffer solution. Appropriate buffers and substrate amounts forparticular restriction enzymes are specified by the manufacturer.Incubation times of about 1 hour at 37° C. are ordinarily used, but mayvary in accordance with the supplier's instructions. After incubation,protein is removed by extraction with phenol and chloroform, and thedigested nucleic acid is recovered from the aqueous fraction byprecipitation with ethanol. Digestion with a restriction enzymeinfrequently is followed with bacterial alkaline phosphatase hydrolysisof the terminal 5' phosphates to prevent the two restriction cleavedends of a DNA fragment from "circularizing" or forming a closed loopthat would impede insertion of another DNA fragment at the restrictionsite. Unless otherwise stated, digestion of plasmids is not followed by5' terminal dephosphorylation. Procedures and reagents fordephosphorylation are conventional (T. Maniatis et al., 1982, MolecularCloning pp. 133-134).

"Recovery" or "isolation" of a given fragment of DNA from a restrictiondigest means separation of the digest on polyacrylamide gelelectrophoresis, identification of the fragment of interest bycomparison of its mobility versus that of marker DNA fragments of knownmolecular weight, removal of the gel section containing the desiredfragment, and separation of the gel from DNA. This procedure is knowngenerally. For example, see R. Lawn et al., 1981, "Nucleic Acids Res."9: 6103-6114, and D. Goeddel et al., 1980, "Nucleic Acids Res." 8: 4057.

"Southern Analysis" is a method by which the presence of DNA sequencesin a digest or DNA-containing composition is confirmed by hybridizationto a known, labelled oligonucleotide or DNA fragment. For the purposesherein, unless otherwise provided, Southern analysis shall meanseparation of digests on 1 percent agarose, denaturation and transfer tonitrocellulose by the method of E. Southern, 1975, "J. Mol. Biol." 98:503-517, and hybridization as described by T. Maniatis et al., 1978,"Cell" 15: 687-701.

"Transformation" means introducing DNA into an organism so that the DNAis replicable, either as an extrachromosomal element or chromosomalintegrant. Unless otherwise provided, the method used herein fortransformation of E. coli is the CaCl₂ method of Mandel et al., 1970,"J. Mol. Biol." 53: 154.

"Ligation" refers to the process of forming phosphodiester bonds betweentwo double stranded nucleic acid fragments (T. Maniatis et al., Id., p.146). Unless otherwise provided, ligation may be accomplished usingknown buffers and conditions with 10 units of T4 ligase ("ligase") per0.5 μg of approximately equimolar amounts of the DNA fragments to beligated.

"Preparation" of DNA from transformants means isolating plasmid DNA frommicrobial culture. Unless otherwise provided, the alkaline/SDS method ofManiatis et al., Id. p. 90., may be used.

"Oligonucleotides" are short length single or double strandedpolydeoxynucleotides which are chemically synthesized by known methodsand then purified on polyacrylamide gels.

All citations are expressly incorporated by reference.

EXAMPLE 1 Isolation Of Cloned Inhibin α-Subunit cDNAs

The strategy for identification of clones containing coding sequencesfor the porcine inhibin subunits was based on the "long-probe" approach,successful in some previous instances (Anderson et al., 1983, "Proc.Nat. Acad. Sci. USA" 80:6836-6842 and Ullrich et al., 1984, "Nature"309:418-425). Briefly, a highcomplexity cDNA library constructed inλgt10 and derived from porcine ovarian mRNA by oligo-dT-primed cDNAsynthesis was screened with a single 64-base-long syntheticoligodeoxynucleotide directed against the N-terminal amino acid sequenceof the α-chain of porcine inhibin. It was found that the library is tobe prepared from fresh ovarian tissue because the inhibin chain mRNA wasapparently quite labile. Approximately 1 in 2,000 plaques hybridizedwith this probe, and sequence analysis of several hybridizing clonedcDNAs confirmed correct probe identification. This analysis revealedthat none of the characterized cDNAs contained sufficient sequenceinformation to predict the complete structure of the α-chain precursorprotein. Rather than analyzing more clones from the same cDNA library, asecond library was constructed by 3' extension on ovarian mRNA of asynthetic oligodeoxynucleotide complementary to a sequenced regionencoding a precursor residues 60-64 (FIG. 1A). This library was screenedwith a suitable restriction fragment from a previously analyzed cDNA andyielded several isolates which specified the remainder of the DNAsequences encoding the N-terminal region of the α precursor.Completeness of the coding sequence was judged from the presence of along reading frame which specifies the porcine α-chain peptide sequenceand starts with a methionine codon preceded by an in-frame stop codonand followed by a hydrophobic sequence bearing the hallmarks of a signalpeptide. The full sequences for the precursor protein and its cDNA areshown in FIG. 1B. The complete protein including signal peptide has anMr of .sup.˜ 40K consisting of 364 amino acids, of which the C-terminal134 (M_(r) .sup.˜ 14.5K) constitute the porcine inhibin α-chain. Thereare several Arg-Arg sequences in the proregion of the precursor, one ofthem directly preceding the α subunit. We believe that this latter pairof basic residues is the processing site for the proteolytic release ofthe α peptide. The deduced precursor sequence predicts two N-linkedglycosylation sites, one within the α chain proper.

In addition to the coding region, the cDNA sequence contains a3'-untranslated sequence of 167 nucleotides, including the canonicalAATAAA polyadenylation signal, and a 5'-untranslated region, the properlength of which is presently unknown.

The detailed method was as follows:

Polyadenylated mRNA was prepared from freshly frozen porcine ovaries(Kaplan et al., "J. Biochem." 183: 181-184). An oligo-dT-primed cDNAlibrary of .sup.˜ 6×10⁶ clones in λgt10 (Huynh et al., 1984, DNA CloningTechniques, Ed. D. Clover) was prepared from 5 μg polyA+ mRNA asdescribed by Wood et al., "Nature" 312: 330-337 (1984), except that theEcoRI adaptors used had the sequence5'-AATTCACTCGAGACGC-3'3'-GTGAGCTCTGCG-5'P.

Approximately 1×10⁶ unamplified cDNA clones were screened with 5α-subunit oligonucleotide5'-ACCGCCCCTTTGCCTTGGCCTTGGTCCCCTGCTGCTCTGAGACTGCTGCAGAGACCTCCTGAGG3',based on the amino acid sequence underlined in FIG. 1B. Hybridizationwas carried out with the phosphorylated ³² P-labelled probe in 5×SSC,40% formamide at 37° C. Filters were washed at 50° C. with 1×SSC, 0.1%SDS. Approximately 500 hybridization positive clones were obtained,twelve of which were purified and examined for insert size. The EcoRlinserts of five of these (λPIN-α2, -α5A, -α5, -α9, -α10) were subclonedinto M13 derivatives (Messing et al., 1981 "Nucl. Acids Res." 9:309-321)and sequenced by the dideoxy chain termination method of Sanger et al.,"Proc. Nat. Acad. Sci. USA" 74:5463-5467 (1977). A specifically primedlibrary was prepared by priming 5 μg of polyA⁺ mRNA with theoligonucleotide 5'-CCCCACAGCATGTCTT-3' (complementary to nucleotides248-263) and subsequent cloning into λgt10. Approximately 2×10⁵ clonesof the 1×10⁶ clones obtained were screened with the 5' 100 bpEcoRI-BamHI fragment prepared from λPIN-α2. Twelve of the 170hybridization positive clones obtained were purified and two (λPIN-S12s,-S4s) were sequenced by the dideoxy method. The complete nucleotidesequences of the α-subunit cDNAs were obtained by subcloning variousrestriction fragments from the different λ isolates into the M13 phagederivatives. Compressions were resolved by the use of deoxyinosine mixesin combination with the E. coli single stranded binding protein(Pharmacia).

Isolation of Cloned Inhibin β Subunit cDNAS

The cDNA sequences encoding the precursors of the inhibin β subunitswere obtained from the same cDNA libraries used for the α subunit.Overlapping cDNA clones were isolated by screening first with singlelong synthetic oligodeoxynucleotide probes based on the two N-terminal βsubunit sequences and subsequently with suitable restriction fragmentsderived from characterized cDNA clones which served as probes for"walking" in both 5' and 3' directions (FIG. 2A).

In more detail, approximately 2×10⁵ oligo-dT primed ovarian cDNA cloneswere screened with the 5' end labelled β_(A) oligonucleotide,5'-AAGAAGCAGTTCTTTGTGTCCTTCAAGGACATTGGCTGGAATGACTGGATCATTGC-3' based onthe amino acid sequence of residues 321-339. Five hybridizationpositives were obtained, of which three proved to contain β_(A) codingsequences (λPIN-βA2, -β_(A) 4, -β_(A) 8). A 5 and 154 bp EcoRI-HindIII(nucleotides 158-297) fragment and a 3' end 213 bp EcoRI-Pst fragment(nucleotides 1679-1892) derived from λPINβ_(A) 2 were used to screen2×10⁶ oligo-dT primed cDNA clones and 2×10⁵ clones from the α-chainspecifically primed library. Out of the sixteen clones analyzed indetail two were found to have longer 5' ends (λPIN-β_(A) 5s, -β_(A) 22)and one clone λPIN-β_(A) 21 contained the entire 3'-untranslated region.Porcine inhibin β _(B) subunit cDNA clones were isolated by screening2×10⁵ clones from the specifically primed library with the β_(B)oligonucleotide5'-GGCCTGGAGTGTGATGGGAGAACCAACCTGTCCTGCCGCCAGGAATTTTTCATCGATTTCAGGCT3',which was based on the NH₂ -terminal sequence described in FIG. 1A.Positive clones were further screened with the oligonucleotide inosineprobe 5'-AAITCTATIAAIAA_(C) ^(T) TG_(C) ^(T) -3' ("I" in this sequencestands for inosine), which covers all the possibilities in thenon-coding strand for the amino acid sequence QQFFIDF. Two clones(λPINβ_(B) -1s, -2s) were isolated and sequenced and found to code forthe β_(B) subunit. A 230 bp EcoRI-Sma (nucleotides 21-251) fragment wasisolated from λPINβ_(B) -I and used as a hybridization probe to screen2×10⁶ oligo-dT primed cDNA clones. Two positives were obtained(λPINβ_(B) -3,4). The nucleotide sequence of these overlapping cloneswas used to construct the sequence shown. All sequences were obtained bysubcloning specific fragments into M13 phage vectors (Messing et al., opcit.). The EcoRI restriction sites referred to above are all containedwithin the cDNA adaptor fragment, and do not refer to sequences presentin the cDNA.

We noted that only very few clones from the oligo-dT-primed library (4out of 2×10⁵) hybridized with the synthetic probe for the β-subunit ofinhibin A. Although most of these proved correct by DNA sequenceanalysis, none contained a full 3'untranslated region, as judged by theabsence of a polyA homopolymer at their 3' ends. Absence of polyA tailssuggested the existence of a very long 3'-untranslated sequence in thismRNA species and/or structural region(s) which prove difficult to copyby the polymerases used for library construction. Unexpectedly, a higherabundance (.sup.˜ 10-fold) of inhibin β_(A) subunit coding sequences wasfound in the cDNA library made by specific priming on αsubunit mRNA.This library was screened with the synthetic probe for the β-chain ofinhibin A on the subsequently refuted theory that the α precursor mRNAmight also encode the β subunit. The high abundance of inhibin β_(A)cDNA in this library was later traced to fortuitous complementarity ofthe specific α chain primer to a region in the 3'- untranslated portionof the corresponding mRNA.

Only four cloned cDNAs encoding the β subunit of inhibin B were found inour libraries. The sequence information obtained from these clonesfailed to reveal the complete structure of the corresponding precursorprotein and its cDNA. The sequences of cDNAs and deduced proteinstructures for the precursors of the β subunits are compared in FIG. 2B.The nucleotide sequence of inhibin β_(A) subunit cDNA is 3.6 kb inlength and contains an open reading frame for a protein of 425 aminoacids (Mr .sup.˜ 46K), the C-terminal 116 residues of which representthe β subunit proper (Mr .sup.˜ 13K). This reading frame begins with amethionine codon followed by a sequence that codes for a characteristicsignal peptide, the true length of which is believed to be 29 residues.The encoded β subunit is preceded by a string of 5 arginines at which itis presumably proteolytically cleaved from the precursor. Similar to theα subunit precursor, this β precursor contains several additional pairsof basic residues at which hitherto unknown biologically active peptideentities are believed to be released. It also contains one possible sitefor N-linked glycosylation in the proregion (Asn, residue 165 ).

The deduced protein sequence for the β subunit of inhibin B shows highhomology with the β_(A) subunit sequence. 71 amino acid residues areidentical and most changes are conservative in nature. Sequencehomology, although of a lesser degree, is also found in the proregion ofboth β subunit precursors. Interestingly, an extremely purine-richsequence rarely seen in coding regions but present in the cDNA encodingthe inhibin β_(A) precursor and resulting in a curious amino acidsequence is not found in the cDNA which codes for the homologous β_(B)precursor. This results in a gap of 22 amino acid residues from theβ_(B) precursor of inhibin when protein sequences are aligned formaximal homology. Such alignment also brings about a perfect match inthe cysteine positions of both precursors (see FIG. 2B).

Northern Analysis of α and β chain Precursor mRNAs

Ovarian total and polyadenylated RNAs were analyzed by the Northernprocedure using the sequenced cDNAs as probes to assess size andrelative abundance of the mRNAs which encode the peptide subunits α andβ and β_(B) of the heterodimeric inhibin molecule. Polyadenylated mRNA(2 μg: lanes a, b, c, and f; 8 μg: lane d) and total RNA (10 μg: lanes eand g) were electrophoresed into a formaldehyde 1.2% agarose gel andblotted onto nitrocellulose filters. The following ³² P-labelled cDNAfragments were used as hybridization probes under stringent conditions.Lane a: 240 bp EcoRI-Sma (nucleotides 134-371) from α subunit cDNA; b:154 pb EcoRI-HindIII (nucleotides 158-297) from βA subunit cDNA; c: 230bp EcoRI-Sma (nucleotides 21-251) from β_(B) subunit cDNA; d and e:EcoRI insert of λPIN-α2; f and g: EcoRI insert of λPIN-β_(A) 5. Filterswere washed for 2 hours with 3 changes of 0.1× SSC, 0.1% SDS at 60° C.

Analysis showed (FIG. 3) that α and β mRNAs are of different size andabundance, as indicated by results obtained from cDNA cloning. Fromtheir respective band intensities the α precursor mRNA is estimated tobe at least of 10-fold higher abundance than the mRNA for the β_(A)precursor, and approximately 20-fold higher than the mRNA for the β_(B)precursor.

Using ribosomal RNAs as size standards, the α precursor mRNA, which is asingle species, is .sup.˜ 1500 nucleotides in length, a size in goodagreement with the cloned cDNA sequence (FIG. 1B). β_(A) precursor mRNAsequences are represented by two main species of .sup.˜ 4.5 and .sup.˜7.2 kg in length. The relatively higher intensity of both species inpolyadenylated than total RNA suggests that the 4.5 kb species does notrepresent 28 S RNA which hybridized to the cDNA probe. Thus, the βprecursor cDNA sequences shown in FIG. 2B are thought to represent the4.5 kb mRNA, suggesting that the 5' untranslated region for the β_(A)mRNA is approximately 900 nucleotides long. The β_(B) precursor isencoded on one mRNA, of approximately 4.5 kb in size, which is presentat roughly half the level of the two β_(A) mRNAs. Since the two β mRNAsare closely related, one can predict that both mRNAs have a similarstructure and thus the β_(B) mRNA presumably possesses a long 5' and 3'untranslated region equivalent to that shown for the β_(A) mRNA. Choiceof a different polyadenylation signal might explain the existence of the7.2 kb species.

Homology To Transforming Growth Factor-β

The mature α and β inhibin subunits contain seven and nine cysteineresidues, respectively. Upon alignment of the cysteine residues it isapparent that the two subunits share a similar cysteine distribution andsome sequence homology exists around these residues (FIG. 4), suggestingthat both types of subunits derive from one ancestral gene.Surprisingly, significant homology was found between the β chain and theprimary structure of human TGF-β recently determined. As outlined inFIG. 4, both peptides are of nearly equal length (inhibin β_(A) subunit,116; β_(B) subunit 115; TGFS, 116 residue) and show a strikingly similardistribution of their nine cysteine residues. Using this cysteine"skeleton" for alignment, the β_(A) and TGF-β sequences have anadditional 31 residues in identical positions and show conservativechanges in nine homologous places. Similar high homologies are seen uponcomparison of the β_(B) and β-TGF. Some gaps were introduced for betteralignment (FIG. 4). The overall homology reaches 35%, but approaches 60%in certain sections (cf. porcine inhibin β.sub. A chain residues 11-45and TGF resides 15-49), a very high degree of homology considering thedifference in species. Interestingly, this homology extends beyond thetermination codon for protein synthesis in the respective cDNAs. Thus,the cDNAs for TGF-β and both inhibin β subunits contain a highly G and Crich sequence in this region, and they also possess unusually long 5'and 3' untranslated regions.

One can discount the suggestion that the β subunit of inhibin is theporcine equivalent of human TGF-β, since there is almost absolutehomology between human and murine β-TGFs. These findings stronglyindicate that both inhibin subunits and TGF-β have a common ancestor andbelong to one gene family. All three peptides are derived fromsimilarly-sized precursors (M_(r) .sup.˜ 40K) where they occupy theC-terminal 100 or so residues and are released by proteolytic cleavageat pairs of arginines. They form homo- or heterodimers, and subunits inthe biologically active complex are linked by disulfide bridges.However, there is little sequence homology between TGF-β and the βsubunits in the pro parts of their precursors, although the regioncomprising the odd residues which precede the β subunit and TGF peptidesdisplay limited but significant sequence relatedness.

EXAMPLE 2 Recombinant Synthesis of Porcine Inhibin

The plasmid used for recombinant synthesis of porcine inhibin waspSVE-PαB_(A) Inh-DHFR. The procedure to construct this plasmid is shownin FIG. 5. This plasmid was constructed as follows:

pHBS348-E (EP 0073656A) was partially digested with EcoRI, blunted withE. coli DNA polymerase I (Klenow fragment) and the four dNTPs, ligatedand the ligation mixture was transformed into E. coli in MM 294 (ATCC31446). The transformed culture was plated on ampicillin media platesand resistant colonies were selected. Plasmids are screened for the lossof the EcoRI site preceding the SV40 early promoter. A plasmid havingthe site deleted is referred to as pHBS348-EII.

pHBS348-EII was digested with EcoRI and EcoRI to produce two fragments,fragment I containing the SV40 early promoter, pmLAmp^(r) sequences andthe HBsAg 3' untranslated region and fragment 2 containing the HBsAg(hepatitis B antigen) coding sequences.

λPINβ_(A) 5_(S) containing the coding region for the porcine inhibinβ_(A) subunit was digested with EcoRI and SmaI and the 1335 bp fragment(fragment 3) containing the β_(A) coding region recovered bypolyacrylamide gel electrophoresis. Fragment I, recovered by agarose gelelectrophoresis, was ligated to fragment 3 and the ligation mixturetransformed into E. coli strain 294 (ATCC 31446). The transformedculture was plated on ampicillin media plates and resistant colonieswere selected. Plasmid DNA was prepared from transformants and checkedby restriction analysis for the presence of the correct DNA fragments.This plasmid is referred to as pSVE-pβ_(A) Inh.

pHBS348-E (EP 0073656A) was partially digested with EcoRI, blunted withE. coli DNA polymerase I (Klenow fragment) and the four dNTPs, andligated to the synthetic oligonucleotide 5' GTCGACC-3' containing theSalI recognition site. The transformed culture was plated on ampicillinmedia plates and resistant colonies were selected. Plasmids werescreened for the presence of the extra SalI restriction site. PlasmidDNA is prepared from this construction (pHBS348-ESalI).

λPINα-12s and λPINα-2 were digested with EcoRI and BamHI. A 104bpEcoRI-BamHI fragment from λPINα-12s containing the 5' coding regionand a 1246 bp EcoRI-BamHI fragment from λPINα-2 containing the middleand 3' coding region were recovered and ligated together. The ligationmixture was digested with EcoRI, the enzyme heat denatured, and themixture ligated to EcoRIdigested pUC9 (BRL). Recombinants were selectedand confirmed by restriction analysis. DNA was prepared from the correctplasmid (pPINα).

pPINα, containing the complete coding region for porcine α-inhibin wasdigested with NcoI and EcoRI, filled in by Pol(I)K in the presence of4dNTP's, and the 1280 bp fragment (fragment 4) was recovered by gelelectrophoresis. pHBS348-ESalI was digested with SstII and HindIII,filled in by Pol(I)K in the presence of 4dNTP's and fragment 5containing the PML-Amp^(r) region, SV40 early promoter and HBsAg 3'untranslated region was recovered by gel electrophoresis. Fragments 4and 5 were ligated together and the ligation mixture was used totransform E. coli 294 (ATCC 31446). Recombinants were selected bygrowing on Ampicillin media plates. The desired recombinant is calledpSVE-PαInh.

pHBS348-ESalI was digested with SalI and HindIII and fragment 6containing the pML-Amp^(r), and SV40 early promoter was recovered by gelelectrophoresis. pFD II (EP 117,060A) was digested with SalI and HindIIIand fragment 7 was recovered which contains the normal mouse DHFR genefused to the HBsAg 3' untranslated region. Fragments 6 and 7 wereligated, and the ligation mixture was transformed into E. coli strain294 (ATCC 31446). The transformed culture was plated on ampicillin mediaplates and resistant colonies were selected. Plasmid DNA was preparedfrom transformants and checked by restriction analysis for the presenceof the correct DNA fragments. This construction is referred to aspFDII-Sall.

pSVE-PαInh was digested with SalI and fragment 8 was recovered whichcontains the SV40 early promoter and the α-inhibin coding region fusedto the HBsAg 3'-untranslated region. pFDIISalI was digested with SalIand fragment 9 containing the SV40 early promoter and the mouse DHFRcoding region linked to the HBsAg 3'-untranslated region was recovered.pSVE-β_(A) Inh was linearized by SalI digestion and ligated to fragments8 and 9 in a three part ligation. The ligation mixture was transformedinto E. coli strain 294 (ATCC 31446). The transformed culture was platedon ampicillin media plates and resistant colonies were selected.Transformants were screened for the presence of fragments 8 and 9 in thecorrect orientation such that transcription from the three SV40 earlypromoters will proceed in the same direction. This final plasmid isdesignated pSVE-Pαβ_(A) Inh-DHFR.

Plasmid pSVE-Pαβ_(A) Inh-DHFR was transfected into DHFR deficient CHOcells (Urlaub and Chasin, 1980, PNAS 77,4216-4220). However, any DHFR⁻mammalian host cell is suitable for use with this plasmid.Alternatively, any mammalian host cell is useful when the host cell iscotransformed with a plasmid encoding neomycin resistance, andtransformants identified by their ability to grow in neomycin-containingmedium.

The transfected CHO cells were selected by culturing in 15 HGT⁻ medium.The cells were allowed to grow to confluency in 15 cm diameter plates.The cells thereafter were cultured in serum free medium for 48 hoursprior to harvest. 50 ml of supernatant medium was lyophilized after theaddition of 100 mg human serum albumin. The residue was redissolved in 3ml 1% fetal bovine serum in HDMEM (GIBCO Laboratories, Santa Clara,Calif.), filtered through a Millex-GS 0.22 mM filter (Millipore Corp.Bedford, Mass.) and assayed in duplicate.

The inhibin hormonal activity in the transformant supernatants wasdetermined by an in vitro bioassay using rat anterior pituitarymonolayer culture, Vale, W. et al. Endocrinology, 91, 562-572 (1972). Inbrief, 21-day-old female rat anterior pituitaries were collected,enzymatically dispersed and plated in 10% fetal bovine serum in HDMEM(GIBCO Laboratories, Santa Clara, Calif.) into 24-well tissue cultureplates (Falcon Plastic, Oxnard, Calif.) on day 1. On day 2, the mediumwas changed to 1% fetal bovine serum in HDMEM, and the transformantmedium sample was added. Incubation was continued for another 48 hours.The monolayer medium was then harvested, and the LH and FSH contentswere determined by radio-immunoassay (RIA) using materials provided byThe Pituitary Hormone Program of NIADDKD. In this assay, theinhibin-containing CHO cell culture inhibits the basal release of FSHbut not LH, as compared to control pituitary cells that received theincubation medium only. The amount of porcine inhibin detected intransformant supernatants was 20 ng/ml and exhibited a dose responsecurve parallel to that obtained with pure porcine ovarian inhibin.

Immunological cross-reactivity is assayed by a sandwichtyperadioimmunoassay. Rabbit antisera are raised against purified porcinefollicular inhibin by s.c. immunization of rabbits with the porcineinhibin in Freund's complete adjuvant. The presence of anti-inhibin inthe antiserum is detected by incubation of the antiserum with purifiedporcine inhibin and assaying for the formation of an immune complex byconventional techniques, e.g. gel filtration. An aliquot of the antiserais coated onto goat-anti-rabbit IgG precoated polystyrene test tubes.The recombinant culture supernatant or extract is diluted into phosphatebuffered saline and added to the coated tubes, incubated overnight andwashed. Another aliquot of the rabbit antiserum is added to the testtubes, incubated and washed. Radioiodinated goat antirabbit IgG is addedto the tubes, incubated and unbound goat antiserum removed by washing.The recombinantly produced inhibin cross-reacts with the rabbitantiserum, as evidenced by bound counts on the test tubes which exceedthose of controls incubated with culture medium or extracts fromuntransformed host cells.

EXAMPLE 3 Construction of Human Inhibin Vector and Expression of HumanInhibin in Recombinant Cell Culture-I

Expression of human inhibin αβ_(A) is facilitated by the discovery thatthe mature porcine and human β_(A) chains are identical. Thus,construction of a vector for the expression of human inhibin can proceedfrom plasmid pSVE-β_(A) -Inh from Example 1, which contains the porcineβ_(A) -encoding cDNA.

A λgt 10 library of human ovarian cDNA made from 10 μg of ovarian mRNAwas subjected to Southern analysis using radiophosphate labelled porcinecDNA encoding α, β_(A) and β_(B) chains. λHINα-2 was identified ascontaining coding regions for the human α inhibin chain. The prevalenceof hybridizing clones in the case of human α inhibin was considerablyless than that found for porcine α inhibin, on the order of 1 in 100,000human clones hybridized to the 685 bp SmaI fragment of the porcine cDNAfor αInh. The β chain clones were also rare, with the β_(B) clones beingpresent at about 3 times the level of β_(A) (1 and 3 out of about1,000,000 clones, respectively). None of the β chain clones were fulllength. They were supplemented with a primed cDNA library and assembledgenerally as described above for the porcine cDNA. The λ inserts wererecovered by EcoRl digestion.

Plasmid pHINα-2 is digested with NcoI and SmaI, and the 1049 bp 15fragment (fragment 10) is recovered by gel electrophoresis. pPinα(Example 2) is digested with EcoRI and PvuII. The 98 bp fragment(fragment 11) is recovered by gel electrophoresis. Fragments 10 and 11are ligated to adaptor I5'-CTGCTCCTCTTGCTGTTGGCCCCACGGAGTGGGCATGGCTGCCAGGGCCCGGAGCTGGACC-3', incombination with adaptor II which is the complement of adaptor I. Theresulting 1208 bp fragment (fragment 12) is treated with Klenow fragmentof Pol(I) and the 4 dNTP's and ligated to pHBS348ESalI which has beenrestricted with HindIII and SacII and bluntended as described inExample 1. Alternatively, pPinα was digested with EcoRI and HpaII, withthe fragment encoding upstream from the HpaII site (that is, the first21 residues of the porcine sequence) being recovered. The adaptor usedin this alternative approach was

5'CGGAGCTCGACC 3'

3' CTCGAGCTGG 5'.

A plasmid pSVE-HαInh having the correct orientation of fragment 12 isidentified by sequence analysis of transformants. This construction(pSVE-HαInh) thus contains the first 24 residues of the porcine signalsequence with the remainder being prepro human inhibin. PlasmidpSVE-HαInh is digested with SalI. The fragment containing the SV40promoter and human inhibin sequence is ligated to fragment 9 and SalIdigested pSVE-β_(A) Inh (Example 2). This final plasmid designatedpSVE-hαβ_(A) Inh-DHFRl is transfected into DHFR-deficient CHO cells andselected as described in Example 2. The culture supernatant containshormonally active human inhibin.

EXAMPLE 4 Construction of Human Inhibin Vector and Expression of HumanInhibin in Recombinant Cell Culture-II

This example is similar to Example 3 except that the pro sequence ofhuman inhibin β_(B) was employed in the place of the porcine β_(B)prepro domain.

The lambda gt10 library of Example 3 yielded λHINα2, as described inexample 3, together with λHINβ_(A) -5 and -14. The latter two phase wereemployed to construct the full length β_(A) coding cDNA by ligating the311 by EcoRl -HindIII fragment (fragment 13) of λHINβ_(A) -5 to the 1101bp HindIII-HpaI fragment (fragment 14) of λHINβ_(A) -14 and ligatingthis mixture in an EcoRlSmal digested mp18 vector (Biolabs). Clones wereselected and screened for the appropriate sized insert. An mp18 vectorcontaining the correct insert was treated with DNA polymerase(I) and thefour dNTPs in order to render it double stranded, and thereafterdigested with XbaI (which cleaves in the mp18 polylinker sequence),blunted with DNA polymerase I and the four dNTPs, and digested withEcoRl. A 1320 bp fragment (fragment 15) was ligated to the EcoRl-EcoRVfragment 1 from Example 2. This ligation mixture was used to transformE. coli 294 cells. Clones were screened by Southern Hybridization andconfirmed by restriction analysis. The clone containing the hInhβ_(A)coding sequence was designated pSVE-humβ_(A) Inh. A plasmid containingthe human β_(A) coding sequences and the human α-inhibin sequencestogether with the DHFR gene is constructed from plasmids pSVE-humβ_(A)Inh, pSVE-HαInh and pFDIISalI as outlined above. Specifically, the Salfragments from pSVE-HαInh and pFDIISalI which contain the human alphainhibin and the DHFR genes were ligated with SalI digested pSVE-humβ_(A)Inh and a clone containing all three genes was identified. This plasmid,designated pSVE-humαβ_(A) Inh-DHFR2, was transfected into DHFR CHO cellsand selected by culture in ght medium. 24 clones were picked, grown toconfluency in ght medium under conditions conventional for CHO cells fortwo days, allowed to rest for 2 more days and thereafter the culturemedia were assayed for inhibin and activin activity using the ratpituitary cell assay describe above. 4 clones were found to secretesignificant levels of human αβ_(A) inhibin (hαβ_(A) -8, 12, 14, and 18).The levels in the culture medium for each clone were, respectively, 125,125, 200 and 250 ng/ml. Another clone (hαβ_(A) -11) produced activin asthe β_(A) β_(A) homodimer, but no detectable inhibin, as determined bybiological activity and the lack of α chain immunoreactivity in theculture medium for this clone. Clone hαβ_(A) -16 secreted only α chainand was devoid of activin or inhibin activity.

EXAMPLE 5 Recombinant Expression of Human Activin

As reported by Vale et al. (Id.) and Ling et al. (Id)., homodimers andheterodimers of the β chains A and/or B have the opposite effect ofinhibin on the pituitary, inducing rather than inhibiting FSH secretion.These proteins, collectively termed activin, are made in α and β chaincotransformants as described in Example 4. However, somewhat lessscreening for an appropriate transformant is needed if the initialtransfection is conducted with a vector or vectors that do not containthe α chain gene. A suitable vector is readily constructed from theabove-described vectors by excising the α chain gene. PlasmidpSVE-humβ_(A) Inh from Example 4 is digested with SalI and ligated tofragment 9 (Example 2) containing the DHFR gene. The ligation mixturewas used to transfect E. coli 294 cells and colonies selected on thebasis of failure to hybridize to the α chain sequence but which didhybridize to the β chain DNA. A clone pSVE-humβ_(A) Inh-DHFR wasidentified from which the α chain DNA had been deleted. This clone istransfected into DHFR CHO cells as described above. Transformants areidentified that secrete activin into the culture medium. Similarly, anexpression vector containing a β_(B) coding sequence (reconstituted byligating DNA encoding the first 34 amino acids of human β_(A) to theremaining coding sequence of the human β_(B) chain) is readilyconstructed and cotransfected with pSVE-humβ_(A) Inh-DHFR to produce theheterodimer. The reconstructed human β_(B) gene also is used in theforegoing plasmids in order to produce αβ_(B) -inhibin which, in the invitro bioassay, has essentially equivalent biological potency to theαβ_(A) form of inhibin.

Although the invention has been described with regard to its preferredembodiments, which constitute the best mode presently known to theinventors, it should be understood that various changes andmodifications as would be obvious to one having the ordinary skill inthe art may be made without departing from the scope of the inventionwhich is set forth in the claims appended hereto.

We claim:
 1. A method for using nucleic acid encoding an inhibin β_(A)chain prodomain polypeptide comprising a sequence selected from thegroup consisting of amino acid residues 1-70, 70-110, 110-180, 180-260,270-309, 28-58, 61-87, 90-108, 111-179, 182-213, 216-258, and 28-87 ofFIG. 2B, and amino acid residues 1-30, 32-40, 43-59, 62-80, 83-185, and186-230 of FIG. 8 to produce the prodomain polypeptide comprising (a)constructing a vector that comprises said nucleic acid, (b) transforminga host cell with the vector, and (c) culturing the transformed cellunder conditions appropriate for expression of said polypeptide.
 2. Themethod of claim 1 wherein the nucleic acid is operably linked to apromoter recognized by the host cell and comprising further the step ofrecovering the polypeptide from the culture medium.
 3. The method ofclaim 2 wherein the cell is a cell from a multicellular organism.
 4. Themethod of claim 2 wherein the promoter is a viral promoter.
 5. Themethod of claim 4 wherein the promoter is an SV40 promoter.
 6. Themethod of claim 1 wherein the cell is a prokaryote.
 7. The method ofclaim 1 wherein the prodomain polypeptide is a porcine inhibin β_(A)chain prodomain polypeptide fragment selected from the sequencesconsisting of amino acid residues 1-70, 70-110, 110-180, 180-260,270-309, 28-58, 61-87, 90-108, 111-179, 182-213, 216-258, and 28-87 ofFIG. 2B, or a human inhibin β_(A) chain prodomain polypeptide fragmentselected from the sequences consisting of amino acid residues 1-30,32-40, 43-59, 62-80, 83-185, and 186-230.
 8. Non-chromosomal DNAencoding an inhibin β_(A) chain prodomain polypeptide comprising asequence selected from the group consisting of amino acid residues 1-70,70-110, 110-180, 180-260, 270-309, 28-58, 61-87, 90-108, 111-179,182-213, 216-258, and 28-87 FIG. 2B, and amino acid residues 1-30,32-40, 43-59, 62-80, 83-185, and 186-230 of FIG.
 8. 9. The DNA of claim8 that is free of intervening untranslated sequences.
 10. The DNA ofclaim 8 that is labeled with a detectable moiety.
 11. Thenon-chromosomal DNA of claim 8 encoding a porcine inhibin β_(A) chainprodomain polypeptide fragment selected from the sequences consisting ofamino acid residues 1-70, 70-110, 110-180, 180-260, 270-309, 28-58,61-87, 90-108, 111-179, 182-213, 216-258, and 28-87 of FIG. 2B, or ahuman inhibin β_(A) chain prodomain polypeptide fragment selected fromthe sequences consisting of amino acid residues 1-30, 32-40, 43-59,62-80, 83-185, and 186-230.
 12. A replicable vector comprising DNAencoding an inhibin β_(A) chain prodomain polypeptide comprising asequence selected from the group consisting of amino acid residues 1-70,70-110, 110-180, 180-260, 270-309, 28-58, 61-87, 90-108, 111-179,182-213, 216-258, and 28-87 of FIG. 2B, and amino acid residues 1-30,32-40, 43-59, 62-80, 83-185, and 186-230 of FIG.
 8. 13. The vector ofclaim 12 comprising a viral promoter operably linked to the DNA encodingthe prodomain polypeptide.
 14. The vector of claim 12 wherein theprodomain polypeptide is a porcine inhibin β_(A) chain prodomainpolypeptide fragment selected from the sequences consisting of aminoacid residues 1-70, 70-110, 110-180, 180-260, 270-309, 28-58, 61-87,90-108, 111-179, 182-213, 216-258, and 28-87 of FIG. 2B, or a humaninhibin β_(A) chain prodomain polypeptide fragment selected from thesequences consisting of amino acid residues 1-30, 32-40, 43-59, 62-80,83-185, and 186-230.
 15. A host cell transformed with a replicablevector comprising DNA encoding an inhibin β_(A) chain prodomainpolypeptide comprising a sequence selected from the group consisting ofamino acid residues 1-70, 70-110, 110-180, 180-260, 270-309, 28-58,61-87, 90-108, 111-179, 182-213, 216-258, and 28-87 of FIG. 2B, andamino acid residues 1-30, 32-40, 43-59, 62-80, 83-185, and 186-230 ofFIG.
 8. 16. The cell of claim 15 that is a eukaryotic cell.
 17. The hostcell of claim 15 wherein the prodomain polypeptide is a porcine inhibinβ_(A) chain prodomain polypeptide fragment selected from the sequencesconsisting of amino acid residues 1-70, 70-110, 110-180, 180-260,270-309, 28-58, 61-87, 90-108, 111-179, 182-213, 216-258, and 28-87 ofFIG. 2B, or a human inhibin β_(A) chain prodomain polypeptide fragmentselected from the sequences consisting of amino acid residues 1-30,32-40, 43-59, 62-80, 83-185, and 186-230.